Field of the Invention
The present invention relates to a wafer processing method for dividing a wafer into a plurality of individual device chips along a plurality of crossing division lines formed on the front side of the wafer, the front side of the wafer being partitioned by the division lines to define a plurality of separate regions where a plurality of devices are formed.
Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines are formed on the front side of a substantially disk-shaped semiconductor wafer to thereby define a plurality of separate regions where a plurality of devices such as integrated circuits (ICs) and large-scale integrations (LSIs) are formed. The semiconductor wafer is cut along the division lines to thereby divide the regions where the devices are formed from each other, thus obtaining individual device chips.
As a method of dividing a wafer such as a semiconductor wafer along the division lines, there has been put into practical use a laser processing method called internal processing using a pulsed laser beam having a transmission wavelength to the wafer, wherein the pulsed laser beam is applied to the wafer in the condition where the focal point of the pulsed laser beam is set inside the wafer in an area to be divided. A wafer dividing method using this laser processing method includes the steps of applying a pulsed laser beam having a transmission wavelength to the wafer in the condition where the focal point of the pulsed laser beam is set inside the wafer, thereby continuously forming a modified layer inside the wafer along each division line, and next applying an external force to the wafer along each division line where the strength has been reduced by the formation of the modified layer, thereby dividing the wafer into the individual device chips (see Japanese Patent No. 3408805, for example).
As a method of applying an external force to the wafer, there is disclosed in Japanese Patent Laid-open No. 2014-17287 a technique including the steps of attaching a protective tape to the front side of the wafer and grinding the back side of the wafer to reduce the thickness of the wafer to a predetermined thickness and simultaneously apply an external force due to grinding to the wafer, so that the wafer is divided into the individual device chips along each division line where the modified layer is formed.